Specifications

THEORY OF OPERATION

The nTrig signal not only wakes the scanner up, but also immediately activates

and turns the scanner into the Operating Mode.

Either nWake or nTrig signals can be used to restart the IS4920-xx103 scanning

engine when the engine is in Power-down Mode, which is indicated by the

asserted (high) PWRDWN signal.

The PWDWN pin is used to indicate when the IS4920 is in various operating

modes such as Power Down, Suspend, and Boot.

Note: The output signals from the IS4920 can experience analog behavior when

VIN is initially applied or removed due to the fact the supply voltage is ramping

up or down. Care must be taken to ensure that this behavior does not adversely

affect the host System. Special attention must be given to the PWRDWN PIN.

When power is initially applied, the output state of this line will be indeterminate

for about 10mS until the USB controller exits reset. This state of this pin should

be disregarded during this time. The following waveforms show several signals

when VIN is first applied (Figure

14) and when VIN is removed (Figure 15).

Figure 14. VIN First Applied